1. Field of the Invention
The present invention relates to an optical disk device and an optical receiver IC (Integrated Circuit), and particularly to a device and an IC which reproduce information from an optical disk such as CD (Compact Disk), DVD (Digital Versatile Disk), and BD (Blu-ray Disk).
2. Description of Related Art
Recently, an optical disk device which reproduces CD, DVD and BD or the like is speeding up. Along with that, an operating frequency band of an optical receiver IC used in the device is increasing the bandwidth. In such an optical disk device, the method described below (hereinafter referred to as a high-frequency superimposing method) is widely used. In the high-frequency superimposing method, a driving current, which a high-frequency signal of approximately 350 to 450 MHz is superimposed thereon, is supplied to a laser light source so as to suppress the influence of noise caused by a laser beam reflected at an optical disk upon being reproduced (the laser beam hereinafter referred to as an optical feedback). Thus, the laser light source oscillates in a multimode.
However, further speeding up could result the operating frequency band of the optical receiver IC to be close to the frequency band of the high-frequency signal, thereby making the high-frequency signal itself a noise source. For example, it is expected to reproduce BD at 12× speed or more, which is an upper limit for the spindle speed. However a frequency of a reproduced signal at 12× speed is 198 MHz, and 200 to 400 MHz band is required as an operating frequency of the optical receiver IC used for detecting the reproduced signal. In order to avoid this problem, the frequency of the high-frequency signal can be increased. However this action is not advisable as it leads to increase in the power consumption, generation of EMI (Electro Magnetic Interference), and increase in the circuit size due to additional components to suppress EMI.
Japanese Unexamined Patent Application Publication No. 2007-73147 (Kikukawa et al.) discloses an optical disk device to deal with the above problem. FIG. 3 shows the configuration of this optical disk device. In the optical disk device la shown in FIG. 3, a laser driver 202 receives a high-frequency signal from an HF oscillator 201, generates a driving current Id on which the high-frequency signal is superimposed, and supplies the driving current Id to a semiconductor laser element 203. Thus, a laser beam L1 is oscillated from the semiconductor laser element 203 in the multimode (namely, the laser beam L1 is in pulse emission).
The laser beam L1 is converted into a parallel beam by a collimator lens 204 and passes through a polarized beam splitter 205 and a quarter wave plate 206. Then, the laser beam L1 is focused over a recording film surface of an optical disk 2 by an objective lens 207. An optical feedback L2 from the optical disk 2 is collected over a photodiode 209 by a focusing lens 208 and converted into a current. This current is converted into a voltage signal (pulse signal) 301 by a current to voltage converting amplifier 210.
Then, a peak hold circuit (P/H) 211 holds the voltage signal 301 at a peak of the pulse emission in synchronization with a control signal from a variable delay line 212 (the control signal is a high-frequency signal from the HF oscillator 201 with its phase difference from the optical feedback L2 being adjusted). A LPF (Low Pass Filter) 213 eliminates a band component (hereinafter sometimes referred to as a high-frequency superimposing component) corresponding to the frequency of the high-frequency signal from an output signal 302 of the P/H 211 (hereinafter sometimes referred to as a peak hold signal) and obtains a temporally continuous reproduced signal 303.
As described above, the optical disk device la is able to eliminate the high-frequency superimposing component.